My favourite is language, not even writing, but language itself. We could collectively invent ways to understand each others with codes shared by tens of millions of individuals, living kilometres apart.

And then I also love early astronomy, like being able to approximate Earth’s circumference (or later the time needed to reach Asia by navigating west), based on the shadow lenght at two fairly distant (but still pretty close) places, thanks to that quirky thing some friends of yours invented to divide land called geometry. To say nothing of those demonstrating Earth rotates around the Sun just by looking at star positions during the year.

As for recent things, something pretty cool we take for granted is radio signals. Information getting places without anything moving, just invisible vibrations through space.